Investigating the effect of temperature gradient on biogas production from pretreated maize straw and rice husk using multistage anaerobic bioreactor

Abstract

The share of biogas in renewable energy sources is increasing as variety of feedstocks are now used for biogas production among which lignocellulosic biomass is emerging feedstock that can be used after proper pretreatment under best suited temperature. Although lot of pretreatments and temperature combinations have been tested but still there is a gap that can be filled by the current study focused on the effect of the temperature gradient (mesophilic and thermophilic) on biogas production potential of maize straw and rice husk using a modified Gompertz equation. Pretreatment was done by using alkali (NaOH and Ca(OH)2) and acids (HCl and H2SO4) each at 2, 4 and 6%.The pretreatment of crop residue with 6% NaOH degraded lignin contents significantly. The pretreated crop residue was further used for biogas production. A multistage anaerobic bioreactor containing three diagonally inline reactors provided with one water bath connected to reactors for better utilization of energy was used for biogas production. The temperature of water bath was adjusted to that the first reactor achieved 37°C and 55 °C for different experiments. The working temperatures found to be 31-37°C and 46-55°C were achieved to maintain the internal temperature of the reactors within mesophilic and thermophilice temperature ranges, respectively. The 36 days incubation time was equally divided for three reactors. The biogas production rate was297 mL/g-VSadded and 244.07 mL/g-VSadded from maize straw and rice husk under mesophilic conditions, respectively. The results showed an increased biogas yield for both feedstocks under mesophilic conditions as compared to thermophilic conditions. The central reactor showed better production as compared to other two rectors in all experiments.